Industrial fan assemblies are used in industrial applications to create fluid flow for processes such as combustion, ventilation, aeration, particulate transport, exhaust, cooling, air-cleaning, drying and air recirculation. Fluid flow is created by rotating an impeller having a plurality of blades to create a reduced pressure at an inlet of the fan assembly to draw air in and an increased pressure at an outlet of the fan assembly to discharge air back into the operating environment. Typically, an industrial fan assembly includes a mounting structure on which a motor and a fan shaft are mounted. A transmission connects the motor to the shaft to convert rotation of a motor shaft of the motor into corresponding rotation of the fan shaft. The impeller is mounted on or otherwise operatively connected to the fan shaft so that rotation of the fan shaft causes rotation of the impeller to generate the fluid flow.
Industrial fans may be generally categorized as being either centrifugal fans or axial fans depending on the flow path of the air passing there through. Centrifugal fans use the rotating impeller to draw air in, typically entering the impeller along an axial path parallel to a rotational axis of the impeller. The air is then redirected to radial flow paths through the impeller blades and out of the fan assembly. The airflow gains kinetic energy as the air moves radially outward toward the impeller blade tips, and the kinetic energy is converted to a static pressure increase beyond the impeller blades causing discharge the air through the fan outlet. Axial fans in contrast move fluid along the rotational axis of the impeller. The fluid is pressurized by the axial forces, or aerodynamic lift, generated by the impeller blades.
The impeller blades of the industrial fan assemblies are subjected to loads and stresses during the operation of the fan assemblies. Where the industrial fan assemblies are implemented in high temperature environments, the impeller blades are further subjected to thermal stresses that, along with the other loads and stresses, can cause the impeller blades to change shape from having a formed radius and blade twist for optimum performance, and thereby result in reduced efficiency and unwanted vibration. These changes can also result in increased sound levels, increased turbulence past the impeller that increases the resistance of the system and the static pressure against which the fan operates. The components of the industrial fan assemblies may also be affected by chemicals and by-products in corrosive atmospheres. Ultimately, the additional thermal stresses and other adverse conditions can result in earlier fatigue failure of the impeller and more frequent need for replacement in high temperature environments as the fan endures numerous thermal cycles from process and in corrosive environments due to exposure to harmful chemicals than when operating in environments that do not cause the same level of thermal stresses or corrosive exposure on the impellers.